Deposition of oxygen vacancy stabilizing the tetragonal ZrO2 catalyst by atmospheric pressure plasma jet: A case study of vanadium redox flow battery application

Tetragonal zirconium dioxide (t-ZrO 2 ) was deposited to graphite felt (GF) electrodes using an atmospheric pressure plasma jet (APPJ) with zirconium nitrate precursor. Plasma diagnostics revealed the presence of reactive species, including Zr, OH, H α , and atomic oxygen, generated from the dissociation of the water-based precursor. These hydrogen-reactive species promoted the oxygen vacancies formation, thereby stabilizing the tetragonal ZrO 2 phase. Structural characterization successfully confirmed the formation of t-ZrO 2 particles on the GF surface, while XPS analysis indicated an increased concentration of oxygen vacancies after plasma deposition. Electrochemical measurements demonstrated significantly enhanced redox kinetics of vanadium ions, with the charge-transfer resistance decreasing from 217.4 Ω for pristine GF to 2.92 Ω under the optimal deposition conditions of 550 W plasma power and 50 scanning cycles. In single-cell vanadium redox flow battery testing, the modified electrode exhibited improved charge-discharge performance and higher energy efficiency of approximately 74-76%, compared with 64-66% for pristine GF. These results demonstrate that APPJ deposition provides a rapid and effective method to stabilize t-ZrO 2 through oxygen-vacancy engineering and significantly enhance VRFB electrode performance.